1. Field of the Invention
The present invention relates in general to a chemical mechanical polishing (CMP) apparatus. In particular, the present invention relates to a pusher for the CMP apparatus.
2. Description of the Related Art
A process commonly used in fabrication of integrated circuits to create a planar topography is chemical mechanical polishing (CMP). This process involves chemically removing a surface while also mechanically grinding or polishing it. The combined action of surface chemical reaction and mechanical polishing allows for a controlled, layer by layer removal of a desired material from the wafer surface, resulting in a preferential removal of protruding surface topography and a planarized wafer surface.
FIG. 1 schematically illustrates a conventional CMP apparatus 100 with a platen 110, a pusher 120, and a wafer carrier 150.
The pusher 120, as shown in FIG. 3, comprises a base disk 134 supported by a support 138, a plurality of guiding structures 122 at the rim of the base disk 134, and a plurality of brackets between the guiding structures 122. The support 138 can lower or raise the pusher 120. Each guiding structure 122 has a shell 124 with an opening 126 (as shown in FIG. 4a), a pin 128 moving through the opening 126, and an elastic device (not shown), such as a spring, for raising and lowering the pin 128. Each pin 128 is a metal bar. The upper part of the pin 128 (as shown in FIG. 4b) is tapered so that the wafer can slide down and be guided to deposit on the brackets 136.
One end of the shell 124 is the opening 126, and the other end is closed. Two fins 130 are disposed at the shell 124 and near the other end of the shell 124. A hole 132 is positioned in each fin 130 so as to connect the guiding structure 122 and the base disk 134.
As shown in FIG. 4c, each pin 128 is put inside the corresponding shell 124 and protrudes from the opening 126. The pin 128 can be lowered and raised by the elastic device. When the pin 128 is pushed, it can be lowered in the shell 124. The opening 126 is rectangular with keyholed corners, as shown in FIG. 4d. 
FIG. 2(a) and (b) show the top view and the side view of the CMP apparatus 100 respectively. The wafer carrier 150 includes a guide ring 152, a top ring 154 and a backing ring 156. The top ring 154 is supported by the backing ring 156, and the guide ring 152 is positioned on the outer periphery of the top ring 154.
A wafer 102 is deposited on the pusher 120 as following. The wafer 102 is deposited on the top of the brackets 136 guided by pins 128 of the guiding structure 122. The pusher 120 is pushed by the support 138 to the wafer carrier 150 and contacts the guide ring 152 of the wafer carrier 150. The pins 128 are lowered into shells 124 so that the wafer 102 can be drawn by vacuum into the space constituted by the guide ring 152 and the backing ring 156. The wafer 102 held by the wafer carrier 150 is transferred to the platen 110.
A polyester polishing pad 112 is positioned on the platen 110, and a slurry from a nozzle 160 is positioned on the polishing pad 112.
The wafer 102 held by the wafer carrier 150 faces downward against the polishing pad 102, and then the platen 110 and the wafer carrier 150 move relative to one another, whereby the surface of the wafer 102 is polished. After polishing, the wafer carrier 150 carries the wafer 102 out of the platen 110 and onto the pusher 120. The pusher 120 is then raised, and the pins 128 of the guiding structures 122 contact the guide ring 152 of the wafer carrier 150. The pins 128 are lowered into shells 124 so that the wafer 102 can be deposited on the top of the brackets 136. The pusher 120 is then lowered.
After polishing, the wafer 102 is washed. However, some slurry may remain on the wafer 102. When the wafer 102 is positioned on the brackets 136 guided by the pins 128, the remaining slurry may flow along the pins 128 into the gap between the pins 128 and the shells 124. If the slurry is dry, some particles are formed at the gap obstructing the movement of the pins 128. The pins 128 cannot guide the wafer 102 normally, and may stick inside the shells 124. In this situation, the wafer 102 cannot be positioned exactly on the top of brackets 136 and parts of the wafer 102 may slide out of the pusher 120. For this reason, when transferring the wafer 102 to the wafer carrier 150, although the wafer 102 can be carried by the wafer carrier 150, the wafer 102 cannot be positioned exactly on the space constituted by the guiding ring 152, and the backing ring 156, as shown in FIG. 5. A part of the wafer 102 is outside the wafer carrier 150. Moreover, the wafer 102 may become deformed due to a vacuum force. When the wafer 102 is polished, a force is applied in the downward vertical direction against wafer 102 and presses the wafer 102 against the polishing pad 112. However, in this situation, the wafer 102 may be broken, and the fragments damage the polishing pad 112 and the backing ring 156. It wastes time and money to shut down the CMP apparatus 100 to clean it.
The present invention provides a chemical mechanical polishing (CMP) apparatus, comprising: a platen with a polishing pad thereon, a wafer carrier, and a pusher. The wafer carrier holds a wafer on the polishing pad, and can move on to and off of the polishing pad. The pusher has a base disk and at least two guiding structures at the rim of the base disk. Each guiding structure has a shell with an opening, an elastic device and a pin moving through the opening, wherein the opening is non-linear.
For the CMP apparatus, a plurality of brackets are disposed between the guiding structures. The opening is composed of two pairs of sides, and at least one pair of sides is concave or convex.